1. Field of the Invention
The present invention relates to a liquid ejection head and liquid ejection apparatus, and more particularly, to a liquid ejection head and liquid ejection apparatus comprising a pressure sensor which determines an ejection defect by determining the ink pressure inside a pressure chamber.
2. Description of the Related Art
As an image forming apparatus, an inkjet recording apparatus (inkjet printer) has been known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (liquid ejection ports) and forms images on a recording medium by ejecting ink (ink droplets) from the nozzles toward the recording medium while the inkjet head and the recording medium are caused to move relatively to each other.
Various methods are known as the ink ejection methods for an inkjet recording apparatus of this kind. For example, a piezoelectric method is known, in which a diaphragm which constitutes a portion of the pressure chamber is deformed by the deformation of a piezoelectric element (piezoelectric ceramic), and thereby the volume of the pressure chamber is changed. Consequently, ink is introduced into the pressure chambers (ink chambers) from an ink supply passage when the volume of the pressure chambers is increased, and the ink inside the pressure chambers is ejected from the nozzles in the form of ink droplets when the volume of the pressure chambers is decreased.
In an image forming apparatus having an inkjet head, such as an inkjet recording apparatus, ink is supplied to the inkjet head via an ink supply channel from an ink tank which stores ink, and this ink is ejected according to one of the various ejection methods described above or another method. In these cases, it is necessary that ink is ejected stably in such a manner that factors such as the ink ejection volume, the ejection velocity, the ejection direction, and the three-dimensional shape of the ejected ink, is adjusted to uniform values at all times.
However, in order that printing can be performed upon issuing a printing instruction, the nozzles of the inkjet head are filled with ink at all times during printing. If the ink in the nozzles is exposed to the air and the ink in nozzles which do not perform ejection for a long period of time dries, then the viscosity of the ink increases. Hence, it may become difficult to eject ink droplets satisfactorily, and nozzle blockages leading to ejection failures may occur. Furthermore, interruption of the ink supply may occur if there is stagnation of air bubbles introduced into the ink supply channels, or the like, and the delay of ink refilling leading to ejection defects may occur if an ejection operation is continued for a long period of time.
For these various reasons, it is necessary to perform maintenance of the ejection head if an ejection failure has occurred or ink is not stably ejected as described above. If maintenance is carried out frequently, then the recording efficiency declines. Therefore, various ways have been proposed for achieving stable ink ejection and stable image recording.
For example, a method is known in which sensors which determine pressure change occurring in the pressure chambers are provided inside the pressure chambers, and the unintentional emission of satellite ink droplets is suppressed by generating a second pressure wave in accordance with the reflected component of the pressure waves determined by the sensors (see, for example, Japanese Patent Application Publication No. 2000-94675).
Furthermore, for example, a method is also known in which a pressure change determination device for determining the pressure waves inside the pressure chambers is provided, and the intrinsic characteristics of the pressure chambers and a drive voltage waveform for ejecting ink droplets suited to these intrinsic characteristics, are calculated on the basis of the pressure waves determined by the pressure change determination device. By ejecting an ejection liquid on the basis of this drive voltage waveform, a drive waveform which is suited to the characteristics of the pressure waves inside the pressure chambers is always applied to the piezoelectric elements (see, for example, Japanese Patent Application Publication No. 7-132592).
Moreover, for example, a method is known in which pressure sensors for determining the pressure inside the pressure chambers are provided between a diaphragm plate and a pressurization mechanism, the pressure applied to the ink inside the pressure chambers is kept uniform at all times in such a manner that the pressure applied by the pressurization mechanism to the diaphragm plate is uniform in accordance with the output determined by the pressure sensors, and hence the quality of the recorded text characters and images is kept uniform at all times (see, for example, Japanese Patent Application Publication No. 5-185590).
However, in the methods described in the above-described references, pressure sensors for determining the ink pressure inside the pressure chambers is provided inside the pressure chambers respectively. If the pressure chambers and the pressure sensors are arranged one-dimensionally in a single layer, and the pressure chambers and the pressure sensors having this structure are arranged at high density in a two-dimensional matrix, then it is difficult to arrange the wires from the pressure sensors at a high density, and therefore it is difficult to achieve high density arrangement of the pressure chambers.
Furthermore, if the wires are arranged at high density, then problems, such as cross-talk arising between adjacent wires, could be expected.